﻿package com.billow.encode
{

　　import flash.utils.ByteArray;

/**
 * base工具 
 * 
 * 
 */		
　　public class Base64 {

　　private static const BASE64_CHARS:String = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";

　　public static const version:String = "1.0.0";

　　public static function encode(data:String):String {

　　// Convert string to ByteArray

　　var bytes:ByteArray = new ByteArray();

　　bytes.writeUTFBytes(data);

　　// Return encoded ByteArray

　　return encodeByteArray(bytes);

　　}

　　public static function encodeByteArray(data:ByteArray):String {

　　// Initialise output

　　var output:String = "";

　　//Create data and output buffers

　　var dataBuffer:Array;

　　var outputBuffer:Array = new Array(4);

　　// Rewind ByteArray

　　data.position = 0;

　　// while there are still bytes to be processed

　　while (data.bytesAvailable > 0) {

　　// Create new data buffer and populate next 3 bytes from data

　　dataBuffer = new Array();

　　for (var i:uint = 0; i < 3 && data.bytesAvailable > 0; i++) {

　　dataBuffer[i] = data.readUnsignedByte();

　　}

　　// Convert to data buffer Base64 character positions and

　　// store in output buffer

　　outputBuffer[0] = (dataBuffer[0] & 0xfc) >> 2;

　　outputBuffer[1] = ((dataBuffer[0] & 0x03) << 4) | ((dataBuffer[1]) >> 4);

　　outputBuffer[2] = ((dataBuffer[1] & 0x0f) << 2) | ((dataBuffer[2]) >> 6);

　　outputBuffer[3] = dataBuffer[2] & 0x3f;

　　// If data buffer was short (i.e not 3 characters) then set

　　// end character indexes in data buffer to index of '=' symbol.

　　// This is necessary because Base64 data is always a multiple of

　　// 4 bytes and is basses with '=' symbols.

　　for (var j:uint = dataBuffer.length; j < 3; j++) {

　　outputBuffer[j + 1] = 64;

　　}

　　// Loop through output buffer and add Base64 characters to

　　// encoded data string for each character.

　　for (var k:uint = 0; k < outputBuffer.length; k++) {

　　output += BASE64_CHARS.charAt(outputBuffer[k]);

　　}

　　}

　　// Return encoded data

　　return output;

　　}

　　public static function decode(data:String):String {

　　// Decode data to ByteArray

　　var bytes:ByteArray = decodeToByteArray(data);

　　// Convert to string and return

　　return bytes.readUTFBytes(bytes.length);

　　}

　　public static function decodeToByteArray(data:String):ByteArray {

　　// Initialise output ByteArray for decoded data

　　var output:ByteArray = new ByteArray();

　　// Create data and output buffers

　　var dataBuffer:Array = new Array(4);

　　var outputBuffer:Array = new Array(3);

　　// While there are data bytes left to be processed

　　for (var i:uint = 0; i < data.length; i += 4) {

　　// Populate data buffer with position of Base64 characters for

　　// next 4 bytes from encoded data

　　for (var j:uint = 0; j < 4 && i + j < data.length; j++) {

　　dataBuffer[j] = BASE64_CHARS.indexOf(data.charAt(i + j));

　　}

　　// Decode data buffer back into bytes

　　outputBuffer[0] = (dataBuffer[0] << 2) + ((dataBuffer[1] & 0x30) >> 4);

　　outputBuffer[1] = ((dataBuffer[1] & 0x0f) << 4) + ((dataBuffer[2] & 0x3c) >> 2);

　　outputBuffer[2] = ((dataBuffer[2] & 0x03) << 6) + dataBuffer[3];

　　// Add all non-padded bytes in output buffer to decoded data

　　for (var k:uint = 0; k < outputBuffer.length; k++) {

　　if (dataBuffer[k+1] == 64) break;

　　output.writeByte(outputBuffer[k]);

　　}

　　}

　　// Rewind decoded data ByteArray

　　output.position = 0;

　　// Return decoded data

　　return output;

　　}

　　public function Base64() {

　　throw new Error("Base64 class is static container only");

　　}

　　}
}